Radiation therapy involves medical procedures that selectively expose certain areas of a human body, such as cancerous tumors, to doses of radiation. The purpose of the radiation therapy is to irradiate the targeted biological tissue such that undesirable tissue is destroyed. Radiation has also been used to obtain image of tissue for planning or treatment purposes.
During a radiation planning session, radiation treatment planning is performed before treatment radiation is delivered to a patient. This allows an accurate and precise dosage of radiation to be delivered to a patient. During the planning session, configuration data, such as location, size, and shape of a target object, may be acquired from an imaging procedure. Such imaging procedure may be performed using existing CT imaging systems, or using other types of medical imaging devices known in the art.
After the radiation treatment plan is determined, the patient then undergoes a radiation treatment procedure. During a radiation treatment procedure, a portion of the patient is imaged, and the obtained image is used to register the patient with the treatment plan. This ensures that a target location prescribed by the treatment plan corresponds with the actual target region of the patient. In some cases, the image that is obtained during the treatment procedure is compared with the reference image that is acquired during the treatment planning phase. If the result of the comparison indicates that the target region is shifted and/or rotated relative to the requirements prescribed by the treatment plan, the patient may be positioned accordingly so that the patient is correctly registered with the treatment plan. After the patient is positioned, a radiation treatment system is used to deliver a desired radiation dosage to the patient according to the determined radiation treatment plan.
Existing systems use rigid registration to register a patient with a treatment plan. Sometimes, such rigid registration may be not work, or may produce unintended result, when non-rigid component is present in the images. Rigid registration algorithms assume that patient may have translated or rotated, but not changed shape or size. For example, a target region may have shifted, rotated, changed shape, and/or changed size, since the treatment planning phase. In such cases, registering a current image of the patient (e.g., one obtained during a treatment phase) with a reference image (e.g., one obtained during the treatment planning phase) may result in the registration model being trapped into a local minimum. For example, if the distance between bone and a target region is different in images, one translation and/or rotation of one image relative to the other can not match both (the bone and the target region) well at the same time. The algorithm may get trapped into a local minimum, where images of the bone matches well, but the images of the target matches poorly, or vice versa. As such, there is a need for systems and methods for improving rigid registration in medical procedures, and more specifically, in radiation procedures.